package com.cyy.servlet;

import com.cyy.annotation.MyAutowired;
import com.cyy.annotation.MyController;
import com.cyy.annotation.MyRequestMapping;
import com.cyy.annotation.MyService;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.*;

/**
 * @Description 手写SpringMVC
 * @Author Crystal
 * @Date 2019/6/24 9:52
 * @Version 1.0
 **/
public class MyServlet extends HttpServlet {

    //保存application.properties配置文件中的内容
    private Properties contextConfig = new Properties();

    //保存扫描到的所有类名
    private List<String> classNames = new ArrayList<String>();

    //保存url和Method的对应关系
    private Map<String,Method> handlerMapping = new HashMap<String, Method>();

    /**
     * 传说中的IOC容器，我们来揭开它的神秘面纱
     * 为了简化程序，暂时不考虑ConcurrentHashMap
     * 主要还是关注设计思想和原理
     */
    private Map<String, Object> ioc = new HashMap<String, Object>();

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //6、调用，运行阶段
        try {
            doDispatch(req,resp);
        } catch (Exception e) {
            e.printStackTrace();
            resp.getWriter().write("500 Exection,Detail : " + Arrays.toString(e.getStackTrace()));
        }
    }

    private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception {
        //绝对路径
        String url = req.getRequestURI();
        String contextPath = req.getContextPath();
        url = url.replaceAll(contextPath,"").replaceAll("/+","/");

        if(!this.handlerMapping.containsKey(url)){
            resp.getWriter().write("404 Not Found!!!");
            return;
        }

        Method method = this.handlerMapping.get(url);
        //投机取巧的方式
        //通过反射拿到method所在class，拿到class之后还是拿到class的名称
        //再调用toLowerFirstCase获得beanName
        String beanName = toLowerFirstCase(method.getDeclaringClass().getSimpleName());

        //为了投机取巧，暂时写死
       Map<String,String[]> params = req.getParameterMap();

       //获取方法的形参列表
        Class<?>[] parameterTypes  = method.getParameterTypes();

        method.invoke(ioc.get(beanName),new Object[]{req,resp,params.get("name")[0]});

    }

    @Override
    public void init(ServletConfig config) throws ServletException {
        //1.加载配置文件
        doLoadConfig(config.getInitParameter("contextConfigLocation"));

        //2.扫描相关的类
        doScanner(contextConfig.getProperty("scanPackage"));

        //3.初始化扫描到的类，并将它们放入IOC容器中
        doInstance();

        //4.完成依赖注入
        doAutowired();

        //5.初始化HandlerMapping
        initHandlerMapping();

        System.out.println("CYY Spring framework is init.");

    }

    //初始化url和Method的一对一对应关系
    private void initHandlerMapping() {
        if(ioc.isEmpty()) { return; }

        //遍历ioc容器
        for(Map.Entry<String,Object> entry : ioc.entrySet()) {
            Class<?> clazz = entry.getValue().getClass();
            //只需要Controller，其他的不要
            if(!clazz.isAnnotationPresent(MyController.class)){continue;}

            //保存写在类上面的@MyRequestMapping("/demo")
            String baseUrl = "";
            if(clazz.isAnnotationPresent(MyRequestMapping.class)){
                MyRequestMapping requestMapping = clazz.getAnnotation(MyRequestMapping.class);
                baseUrl = requestMapping.value();
            }

            //默认获取所有的public方法
            for(Method method : clazz.getMethods()){
                if(!method.isAnnotationPresent(MyRequestMapping.class)){continue;}

                MyRequestMapping requestMapping = method.getAnnotation(MyRequestMapping.class);
                //默认用户没有输入 '/query'而输入'query'，自动给加上'/',如果用户输入了多个'/'，则去掉，只保留一个'/';
                String url = (baseUrl + "/" + requestMapping.value())
                        .replaceAll("/+","/");
                handlerMapping.put(url,method);
                System.out.println("Mapped :" + url + "," + method);
            }
        }
    }

    //自动依赖注入
    private void doAutowired() {
        if(ioc.isEmpty()){ return; }

        for(Map.Entry<String, Object> entry : ioc.entrySet()){
            //Declared 所有的，特定的 字段，包括private/protected/default
            //正常来说，普通的OOP编程只能拿到public的属性
            Field[] fields = entry.getValue().getClass().getDeclaredFields();
            for(Field field : fields){
                if(!field.isAnnotationPresent(MyAutowired.class)){continue; }
                MyAutowired autowired = field.getAnnotation(MyAutowired.class);
                //如果用户没有自定义beanName，默认就根据类型注入
                //TODO 这个地方省去了对类名首字母小写的情况的判断,待完善
                String beanName = autowired.value().trim();
                if("".equals(beanName)){
                    //获得接口的类型，作为key待会拿这个key到ioc容器中去取值
                    beanName = field.getType().getName();
                }

                //如果是public以外的修饰符，只要加了@Autowired注解，都要强制赋值
                //反射中叫做暴力访问
                field.setAccessible(true);

                try {
                    //用反射机制，动态给字段赋值
                    field.set(entry.getValue(),ioc.get(beanName));
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private void doInstance() {
        //初始化，为DI做准备
        if (classNames.isEmpty()) {
            return;
        }

        for (String className : classNames) {
            try {
                Class<?> clazz = Class.forName(className);

                //什么样的类才需要初始化呢？
                //加了注解的类，才初始化，怎么判断？
                //为了简化代码逻辑，主要体会设计思想，只举例 @Controller和@Service,
                // @Componment...就一一举例了
                if (clazz.isAnnotationPresent(MyController.class)) {
                    Object instance = clazz.newInstance();
                    //Spring默认类名首字母小写
                    String beanName = toLowerFirstCase(clazz.getSimpleName());
                    ioc.put(beanName, instance);
                } else if (clazz.isAnnotationPresent(MyService.class)) {
                    //1.自定义的beanName
                    MyService service = clazz.getAnnotation(MyService.class);
                    String beanName = service.value();
                    //2.默认类名首字母小写
                    if ("".equals(beanName.trim())) {
                        beanName = toLowerFirstCase(clazz.getSimpleName());
                    }
                    Object instance = clazz.newInstance();
                    ioc.put(beanName, instance);
                    //3.根据类型自动赋值
                    for (Class<?> i : clazz.getInterfaces()) {
                        if (ioc.containsKey(i.getName())) {
                            throw new Exception("The “" + i.getName() + "” is exists!!");
                        }
                        //把接口的类型直接当成key了
                        ioc.put(i.getName(), instance);
                    }
                } else {
                    continue;
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }

    //如果类名本身是小写字母，确实会出问题
    //但是我要说明的是：这个方法是我自己用，private的
    //传值也是自己传，类也都遵循了驼峰命名法
    //默认传入的值，存在首字母小写的情况，也不可能出现非字母的情况

    //为了简化程序逻辑，就不做其他判断了，大家了解就OK
    //其实用写注释的时间都能够把逻辑写完了
    private String toLowerFirstCase(String simpleName) {
        char[] chars = simpleName.toCharArray();
        //之所以加，是因为大小写字母的ASCII码相差32，
        // 而且大写字母的ASCII码要小于小写字母的ASCII码
        //在Java中，对char做算学运算，实际上就是对ASCII码做算学运算
        chars[0] += 32;
        return String.valueOf(chars);
    }

    /**
     * 扫描出相关的类
     *
     * @param scanPackage: com.cyy.demo,存储的是包路径
     * @throws
     * @author Crystal
     * @date 2019-07-03 07:44:04
     * @return: void
     */
    private void doScanner(String scanPackage) {
        //将包路径转换为文件路径
        URL url = this.getClass().getClassLoader().getResource("/" + scanPackage.replaceAll("\\.", "/"));
        File classPath = new File(url.getFile());
        for (File file : classPath.listFiles()) {
            if (file.isDirectory()) {
                doScanner(scanPackage + "." + file.getName());
            } else {
                if (!file.getName().endsWith(".class")) {
                    continue;
                }
                String className = (scanPackage + "." + file.getName().replace(".class", ""));
                classNames.add(className);
            }
        }
    }

    /**
     * 加载配置文件
     * 直接从类路径下找到Spring主配置文件所在的路径
     * 并且将其读取出来放到Properties对象中
     * 相对于scanPackage=com.cyy.demo 从文件中保存到了内存中
     *
     * @param contextConfigLocation: 配置文件位置
     * @throws
     * @author Crystal
     * @date 2019-07-03 07:38:57
     * @return: void
     */
    private void doLoadConfig(String contextConfigLocation) {
        InputStream is = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation);
        try {
            contextConfig.load(is);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (null != is) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}
